What is the difference between dye-based and pigment-based inks?

The two primary types of fountain pen inks differ mainly in how the colorant is formulated:

Dye-based inks consist of soluble dyes dissolved in a liquid solvent (usually water). These inks are known for providing vibrant, luminous colors and are generally easier to clean. However, they are water-sensitive and can fade or run if exposed to moisture.

Pigment-based inks contain tiny, solid particles suspended in the liquid. Because these pigments do not dissolve, they sit on the paper’s surface and are more resistant to water and fading. The trade-off is that pigment inks may require more frequent cleaning, as their particles can accumulate and clog the pen's feed. The choice between dye and pigment often depends on your needs—if you prefer bold colors with easy maintenance, dye inks are ideal; for archival documents or artwork requiring water resistance, pigment inks might be preferable.